Cellular wireless communication systems support wireless communication services in many populated areas of the world. While cellular wireless communication systems were initially constructed to service voice communications, they are now called upon to support data and video (multimedia) communications as well. The demand for video and data communication services has exploded with the acceptance and widespread use video capable wireless terminals and the Internet. Video and data communications have historically been serviced via wired connections; cellular wireless users now demand that their wireless units also support video and data communications. The demand for wireless communication system video and data communications will only increase with time. Thus, cellular wireless communication systems are currently being created/modified to service these burgeoning demands.
Cellular wireless networks include a “network infrastructure” that wirelessly communicates with wireless terminals within a respective service coverage area. The network infrastructure typically includes a plurality of base stations dispersed throughout the service coverage area, each of which supports wireless communications within a respective cell (or set of sectors). The base stations couple to controllers, with each controller serving a plurality of Node B's. Each controller couples to a mobile switching center (MSC). Each controller also typically directly or indirectly couples to the Internet. In the 3rd Generation Partnership Agreement (3GPP) these base stations may also be referred to as “Node B's” and the wireless terminals may be referred to as user equipment (UE).
In operation, each Node B communicates with a plurality of wireless UEs operating in its cell/sectors. A controller coupled to the Node B routes voice, video, data or multimedia communications between the MSC and a serving base station. The MSC then routes these communications to another MSC or to the PSTN. Typically, controllers route data communications between a servicing Node B and a packet data network that may include or couple to the Internet. Transmissions from base stations to wireless terminals are referred to as “forward link” or “downlink” transmissions while transmissions from wireless terminals, or user equipment, to base stations are referred to as “reverse link” or “uplink” transmissions. The volume of data transmitted on the forward link typically exceeds the volume of data transmitted on the reverse link. Such is the case because data users typically issue commands to request data from data sources, for example, web servers, and the web servers provide the data to the wireless terminals. The great number of wireless terminals communicating with a single Node B forces the need to divide the forward and reverse link transmission resources (depending on the specific wireless standards, the resources could be frequency band, time slot, orthogonal code, and transmit power) amongst the various wireless terminals.
Wireless links between base stations and their serviced wireless terminals typically operate according to one (or more) of a plurality of operating standards. These operating standards define the manner in which the wireless link may be allocated, setup, serviced and torn down. One popular cellular standard is the Global System for Mobile telecommunications (GSM) standard. The GSM standard, or simply GSM, is predominant in Europe and is in use around the globe. The GSM standard has evolved in part into the 3rd Generation Partnership Agreement (3GPP). 3GPP provides Technical Specifications and Technical Reports for a 3rd Generation Mobile System based on evolved GSM core networks and the radio access technologies that they support (that is, UMTS Terrestrial Radio Access (UTRA) both Frequency Division Duplex (FDD) and Time Division Duplex (TDD) modes). The scope also includes the maintenance and development of the Global System for Mobile communication (GSM) Technical Specifications and Technical Reports including evolved radio access technologies (for example, General Packet Radio Service (GPRS) and Enhanced Data rates for GSM Evolution (EDGE)). While GSM originally serviced only voice communications, it has been modified to also service data communications. General Packet Radio Service operations and the Enhanced Data rates for GSM (or Global) Evolution (EDGE) operations coexist with GSM by sharing the channel bandwidth, slot structure, and slot timing of the GSM standard. GPRS operations and EDGE operations may also serve as migration paths for other standards as well, for example, IS-136 and Pacific Digital Cellular (PDC).
Third generation (3G) cellular networks have been specifically designed to fulfill the future demands of the mobile Internet. As mobile Internet services grow in popularity and usage, factors such as cost efficient optimization of network capacity and quality of service (QoS) will become ever more essential to cellular operators. These factors may be achieved with careful network planning and operation, improvements in transmission methods, and advances in receiver techniques. To this end, carriers need technologies that will allow them to increase uplink and downlink throughput and, in turn, offer advanced QoS capabilities and speeds that rival those delivered by cable modem and/or DSL service providers. In this regard, networks based on Wideband CDMA (WCDMA) technology can make the delivery of data to end users a more feasible option for today's wireless carriers. WCDMA has evolved continuously towards higher data rates and towards packet-switched IP-based services.
GPRS and EDGE technologies may be utilized for enhancing the data throughput of present second generation (2G) systems such as GSM. The GSM technology may support data rates of up to 14.4 kilobits per second (Kbps), while the GPRS technology may support data rates of up to 115 Kbps by allowing up to 8 data time slots per time division multiple access (TDMA) frame. The EDGE technology, a further enhancement to GPRS, may support data rates of up to 384 Kbps. The EDGE technology may utilizes 8 phase shift keying (8-PSK) modulation to provide higher data rates than those that may be achieved by GPRS technology. The GPRS and EDGE technologies may be referred to as “2.5G” technologies.
UMTS technology with theoretical data rates as high as 2 Mbps, is a 3G evolution of GSM, using Wideband CDMA technology. UMTS may achieve higher data rates than GSM/EDGE due to many enhancements, including higher transmission bandwidth, adaptive higher order modulation and interference averaging due to a unity frequency reuse factor.
High-Speed Downlink Packet Access (HSDPA) technology is an Internet protocol (IP) based service, oriented towards data communications, which adapts WCDMA to support data transfer rates in the order of 14 megabits per second (Mbit/s). Developed by the 3G Partnership Project (3GPP) group, the HSDPA technology achieves higher data rates through a plurality of methods. In order to avoid excessive interference, 3G WCDMA may require fast power control to maintain a constant error rate. The HSDPA technology changes this paradigm and, in addition to adapting transmission power, also change the coding and modulation rate to adapt to changing channel conditions. Other methods that may be used to improve the data throughput are fast packet scheduling and a fast retransmission of lost packets by using Hybrid Automatic Repeat Request techniques.
For the HSDPA application, downlink data can be transmitted on the HS-DSCH, therefore legacy WCDMA DPCH channel is not necessary. But on the uplink, user equipment (UE) may still use DPCH to communicate to the Node B (or serving node), so it still needs to be power controlled. This requires that on the downlink the Transmit Power Control (TPC) bits in the DPCCH need to be preserved. In light of this, the fractional DPCH (F-DPCH) is introduces where only TPC bits are transmitted in the downlink. An additional benefit of this is that multiple users can use the save orthogonal spreading code if they all use F-DPCH, as they can be time multiplexed.
Since for F-DPCH in the downlink, only TPC is transmitted and dedicated pilot bits are no longer present, numerous processing in the UE, such as Signal-to-Interference Ration (SIR) estimation, power control target setting, frame sync process need to be redesigned.